Centrifugal snap-action mechanism



Oct. 12, 1954 R. A. FISCHER P CENTRIFUGAL SNAP-ACTION MECHANISM Filed Dec. 51, 1949 3 Sheets-Sheet 1 2736 O 3 Q m 4% /2 l M V l3 9/ 6 FF 6/ 5-972 70 48 43 34 A will! a 53 A 64-' 58 92 5/ 35 22 23 4 /4. mi if 47 .52 63 Z5 6; Z 1 Z4 r II lo a 26 /0 HQ Z7 Z9 Fi 3. l A

INVENTOR.

Oct. 12, 1954 R. A. FISCHER CENTRIFUGAL SNAP-ACTION MECHANISM 3 Sheets-Sheet 2 Filed Dec. 31, 1949 [NOE/Won RIC/MR0 H. FISCHER BY HIS HTTO/VNEYS. HARP/5, K/ECH, FOSTER &HAAIP/5 Oct. 12, 1954 Filed Dec. 31, 1949 FORCES HPPL/ED TO ARM 4O R. A. FISCHER CENTRIFUGAL SNAP-ACTION MECHANISM 3 Sheets-Sheet 3 F55maX- \93 8/ I \[j90 /\V/ I (p L e ;4

, INVENTOR.

ANGLE OF ARM 4O R/cHA/w AF/ScI-IE/P BY HIS ATTORNEYS.

Patented Oct. 12, 1954 UNITED STATES -PATENT OFFICE CENTRIFUGAL SNAP-ACTION MECHANISM Richard A. Fischer, Los Angeles, :Calif., assignor to The Garrett Corporation, LosAngelcs, Calif., .a corporation of California Application December 31, 1949, Serial 'No. 136,345

9 Claims. 1

centrifugal ,force is applied .to the weight to operate the snap-action mechanism.

Another object is to provide a device of the foregoing character which includes a support, an arm which is pivotally connected at one end to the support and which is free to move relative to the support at its other end, a weight carried by the arm, spring means for biasing the :arm in one direction relative .to the support, and means for rotating the support about an axis such that a centrifugal force is applied to the weight car- .ried by the arm to bias the arm in the opposite direction relative to the support.

Still another object is to provide such a device wherein the axis of .rotation of the support makes an angle of less than 90 with .a reference line extending from the point of pivotal connectionof the arm to the combined center of gravity of the arm and the weight so that a centrifugal force applied to the arm is developed upon ro- I tation of the support.

A further object is to provide two stops carried by the support and respectively disposed on opposite sides of the arm to limit movement of the arm relative to the support, the arm being biased toward one of the stops by the spring force applied thereto by the spring means and the arm being biased toward the other of the stops by the centrifugal force developed upon rotation of the support.

Another object is to provide a device wherein the spring means comprises a leaf spring which is in longitudinal compression and which is connected at one end to the arm and at its other end to the support. More specifically, an object in this connection is to provide a spring means wherein the leaf spring is connected to the free end of the arm and is pivotally connected to the support intermediate the ends of the arm.

Still another object is to provide a device of Cit the character set forth which includes a stationary switch spaced from the rotatable support :and which includes actuating means operatively' connecting the aforementioned arm of the snap-action mechanism and the switch for actuating the switch.

Another object is to provide stationary resilient means spaced from the rotatable support and acting on the aforementioned actuating means for opposing the centrifugal force applied to the arm of the snap-action mechanism and for aiding the'spring force applied thereto by the aforementioned spring means.

An object in connection with one embodiment of the invention is to provide a device wherein the resilient means which acts on the arm of the snap-action mechanism through the aforementioned actuating means is incorporated in the switch.

An object in connection with another embodiment of the invention is to provide a device wherein the resilient means acting on the arm .of the snap-aotion mechanism through the aforementioned actuating means is independent of the switch.

.As will be apparent, a device embodying the fundamental principle of the invention as outlined .by the foregoing objects is responsive to the rotational speed of the support and operates whenever the rotational speed of the support .reaches a critical value such that the centrifugal force applied to the arm of thesnap-action mechanism exceeds the spring force applied thereto. The device maybe employed wherever response to a predetermined critical rotational speed is desired, one possible use of the device being to prevent overspeeding of an apparatus with which it is associated, in which case the device acts as a governor. For example, the aforementioned switch may be employed to operate some means for interrupting, or decreasing, the delivery of fuel to an engine whenever the switch is actuated by the snap-action mechanism. However, it will be understood that the utility of the device is not limited to a governing action. Also, for other applications of the device, it will be understood that the actuating means operatively connecting the arm of the snap-action mechanism to the switch may be employed to operate an element other than a switch, if desired.

As indicated above, the device of the invention is responsive to a predetermined critical rotational speed and an important object of the invention is to provide adjusting means for varying the critical rotational speed to which the device is responsive.

The foregoing objects and advantages of the present invention, together with various other objects and advantages thereof which will become apparent, may be attained through the utilization of the exemplary embodiments of the invention which are illustrated in the accompanying drawings and which are described in detail hereinafter. Referring to the drawings:

Fig. 1 is a longitudinal sectional view of a devic which embodies the centrifugally-operated snap-action mechanism of the invention;

Fig. 2 is a view which is partly in transverse section and which is taken along the broken line 22 of Fig. 1;

Fig. 3 is a transverse sectional view which is taken along the broken line 33 of Fig.1;

Fig. 4 is an enlarged, fragmentary sectional view which is taken along the broken line 4-4 of Fig. 3;

Fig. 5 is a diagrammatic view of the centrifugally-operated snap-action mechanism of the in vention;

Fig. 6 is a diagram illustrating the operation of the centrifugally-operated snap-action mechanism of the invention; and

Fig. 7 is a fragmentary sectional view similar to Fig. 1 but illustrating another embodiment of the invention.

Referring particularly to Figs. l and 2, the numeral designates a housing having a mounting flange H for attachment to an apparatus with which the invention is associated. The housing l0 provides a chamber |2 which is open at its ends, one end of the chamber being closed by a plug-like closure |3 which is connected to the housing by bolts l4 and the other end of the chamber being closed by a plate-like closure I which is connected to the housing by screws I6. A cup-like housing element I! is attached to the housing it over the closure l5 by screws l8.

Pressed into a bore in the plug-like closure I3 is a bearing 2| for a shaft 22 having a gear 23 thereon, the shaft being retained in the bearing by a thrust plate 24 which engages the gear 23 and which is secured to the housing ID by one or more bolts 25. Meshed with the gear 23 on the shaft 22 is a gear 26 on a cross shaft 2'! which is mounted in bearings 28 and 2 9 and which projects from the housing I!) at one end, the meshing of the gears 23 and 26 being illustrated diagrammatically. The projecting end of the cross shaft 2! may be operatively connected in any suitable manner to an apparatus with which the invention is associated so that such apparatus drives the shaft 22 through the cross shaft 21 and the gears 23 and 26. It will be understood that the particular driving means shown for th shaft 22 is merely illustrative and that the shaft 22 may be driven in any desired manner by the apparatus with which the invention is associated.

Considering the invention in more detail, it includes a support 33 having a stem 34 which is disposed in a bore in the shaft 22 and which is retained therein by a pin 35 so that the support rotates with the shaft 22 about the axis of -rotation AA thereof. Mounted on the support 33 is a snap-action mechanism which includes an arm 40, the latter being a tension member of the mechanism and being illustrated as a leaf spring. One end 4| of the arm 40 is connected to the support 33 on one side of the axis of rotation AA by means of a screw 42 which is threaded through an opening in the support and secured by a nut 43. The screw 42 extends through an opening in the end 4| of the arm 40 which is slightly enlarged relative to the diameter of the screw adjacent the head thereof, the screw 42 having a reduced neck 42a adjacent its head which is disposed in the opening in the end 4| of the arm. This construction produces the effect of an adjustable pivotal connection between the arm 40 and the support 33, which effect is enhanced by the flexibility of the leaf spring preferably employed for the arm 40. It will of course be apparent that the arm 40, conveniently a leaf spring, is nevertheless fundamentally a tension member and need not be a leaf spring, but may be a wire, chain, cable, or the like. It will be understood that, by employing a flexible member for the arm 40, the effect of a pivotal connection between the arm and the support 33 will be attained even if the end 4| of the arm is connected to the support 33 in cantilever fashion.

The support 33 carries stops 46 and 41 for limiting pivotal movement of the arm 40 relative to the support, the stops being disposed on opposite sides of the arm. As best shown in Figs. 1 and 3, the stop 46 is formed by a bridge which spans and is formed integrally with lugs 48 on the support 33. The stop 4'! is formed by a surface of the support 33 which would, if extended, intersect the axis of the screw 42 at a point outwardly of the head of the screw. Consequently, when the arm 40 is biased toward the stop 41 in a manner to be described, the arm first contacts the end of the surface defining the stop 47 which is nearest the screw 42, the arm thereafter flexing as it is biased into engagement with the stop 41, which is the normal position of the arm. Thus, with this construction, the pivoted end 4| of the arm 40 is biased into engagement with the neck 42a of the screw 42 when the arm 40 is in its normal position so as to fix the point of pivotal connection of the pivoted end 4| relative to the screw. It will be understood that the surface of the support 33 may be formed so that only that portion of the arm 40 distal of its pivoted end 4| engages the stop 4'! when the arm is biased thereto. In that event the arm 40 would not be bowed in the manner shown in Figs. 1 and 'I.

The arm 40 is biased toward the stop 41 by a compression spring means which includes a pair of leaf springs 5|. Th springs 5| are disposed on opposite sides of the arm 40 and are connected to the free end 52 of the arm, preferably by being formed integrally therewith as best shown in Fig. 3. It will be noted that, in the particular construction illustrated, the free end 52 of the arm '40 is disposed on the opposite side of the axis A-A from the pivoted end 4| of the arm. The opposite ends of the springs 5| are pivotally connected to the support 33 by being disposed in notches 53 in the lugs 48 on the support, as best shown in Figs. 1 and 4, the points of pivotal connection of the springs to the support being intermediate the pivoted and free ends 4| and 52 of the arm 40 and being disposed on one side of the arm when the latter is in its normal position. The length of the springs 5| is greater than the distance between their points of pivotal connection to the lugs 48 and their points of connection to the arm 4|! so that they are in longitudinal compression. When the arm 40 is in its normal position, the springs 5| are 5 bowed as illustrated to bias the arm toward the stop 41.

As will be apparent, the arm 40 and the springs 5| cooperate-to provide a snap-action mechanism which is more or less conventional, motion ofthe mechanism being limitedby the stops 46 and 41; In the particular construction illustrated, the stop 46 is so located relative to the points of pivotal connection'of the springs 5| to the support 33 that the snap-action mechanism does not move over center as the arm 40 moves from the stop 4'! to the stop 46, i. e., is so located that 'thearm 40 does not traverse the points "of pivotal connection of the springs to the support. Thus, the springs 5| continually bias the arm 40 toward the stop 41. However, it will be understood that, if desired, the stop 45 may be so positioned relative to the points of pivotal connection of the springs 5i to the support that the snap-action mechanism does move over center in moving from the stop '4 to the stop 46 without departing from the spirit of the invention.

The snap-action mechanism is operable by a centrifugal force applied thereto in a direction to bias the arm Ml toward the stop it upon rotation of the support 33 about the axis A-A, the centrifugal force biasing the arm Ml toward the stop 415 and the spring force biasing the arm toward the stop 41 being in opposition, The centrifugal force is obtained by providing a weight '55 on the free end 52 of the arm 40 in the particular construction illustrated. In order to obtain thedesired centrifugal force, it is necessary that the axis of rotation A-A of the support 33 make an angle of less than 90 with a reference line extending between the pivoted end 4| of the arm 40 and the combined center of gravity of the arm All and the Weight 55, thereby providing a centrifugal force component in a direction generally parallel to the axis A-A. Since the arm 40 is substantially weightless as compared to the weight 55, the resultant center of gravity of the arm and the weight substantially coincides with the center of gravity of the weight per so.

In the particular application of the invention illustrated, the centrifugally-operated snap-action mechanism is employed to actuate a'switc'h :56 which is disposed within the housing element H, the switch 58 comprising a post 5'! of insulating material which is mounted on the plate like closure I 5 of the housing It. The switch also includes spring blades 58 and 59 which are mounted on the post 51 in cantilever fashion and which carry contacts titan-d iii, the contacts normallv being spaced apart so that the switch is open. The blades 58 and '59. are connected to terminals 62 and 63 by wires 64 and 65, the terminals being mounted on the housing element H.

The switch 56 is actuated by an actuating means 10 which operatively connects the centrifugally-actuated snap-action mechanism to the switch, the actuating means I comprising a plunger H one end of which is adapted to be engaged by the arm ill of the snap-action mechanism and the other end of which is provided with a head :2 adapted to engage the switch blade 59. The plunger TI is reciprocable in a tubular guide 13 which is threaded into the plate-like closure I of the housing Hi. In the particular construction illustrated, the plunger H is normally spaced from the arm 46 to minimize wear, the arm lbeingadapted to engage the plunger to close the switch '56 as the arm moves from the 6 stop toward-the stop 46'; The switch 56 is insulated relative to the snap-action mechanism iii-any suitable manner, as by making the plunger 1 l of' an insulating material.

The operation of the invention will now be considered with particular reference to Figs. 5 and 6 of the drawings. Referring first to Fig. 5, the reference character 6 designates the angle through which the arm 46 moves in rotating from its on-center position, designated bythe referenceline 78, into its normal position wherein it engages the stop 41, the angle 0 being regarded as zero when thearm is in its oncenter position. However, in the particular construction illustrated, the angle 0 can never attain a value of zero since the stop 46 prevents the arm- 40 from attaining its on-center position. The reference character designates the angle between the arm 40 and a line H perpendicular to the axis of rotation AA of the support 33 and intersecting the point of pivotal connection of the arm '40 to the support. The angle' b is zero at the perpendicular line 71 and is a maximum at the point where 6 is a maximum.

Continuingto refer to Fig. 5, the springs 5| apply a spring force to the arm 40' which biases it toward the stop -41 aspreviously indicated, the spring force being designated by the arrow F51. When thesupport 33 is rotated about the axis-A--A, a centrifugal force, designated by the arrow '18, is applied to the weight 55 in a direction normal to the axis A-A. This centrifugal force may be resolved into a component 59 parallel to the arm ii] and a component F55 perpendicular thereto, the centrifugal force component F55 biasing the arm 40 toward the stop' l6 and being opposed to the spring force F51. As will be apparent, the arm at moves in the direction of the'larger of the two forces F51 and F55 as will be discussed in more detail hereinafter.

Referring now to'Fig. 6, the forces F51 and F55 applied to the arm lil are graphically related to the angles o and 0 of the arm. As will be apparent, the 'value of F51 is zero at the point 81' where 0 is zero, i. e., at the 0I1-C8Ilt6r position of the arm M). The value of F51 increases with increases in the value of 0 (01" from the point 81 where t1 and 6 areequal to zero.

In Fig. 6, the relationship between F55 and the angle of the arm Mi relative to the perpendicular is illustrated graphically for two rotational speeds of the support 33, the force-angle relationship for the higher rotational speed being designated as Fra and the relationship for the lower rotational speed being designated by Fss As will be apparent, [F55 and Fss are equal to zero when rt is zero and increase substantially linearly as 6 (or increases.-

In Fig. 6, the value of 0 corresponding to the position of the arm 40 when it is in engagement with the stop is illustrated graphically bythe vertical dotted line 046. Similarly, the value of 0 corresponding to the normal position of the arm wherein it engages the stop 4? is illustrated graphically by the vertical dotted line 947. It will be noted that since, in the particular construction-illustrated, the stop 36' prevents the arm 48 from reaching on-center position wherein the Value of 0 is zero, the line 646 intersects thehori zontal axis of the graph at a value of 0 which is greater than zero.

Considering the operation of the invention in connection with 6, it will be assumed that the device of the invention is operating at a point 82 'on the-line 647. Under such. conditions,

the arm 40 is in engagement with the stop 41 and the support 33 is rotating at a speed such that F51 exceeds F55 so that the arm is continually biased into engagement with the stop 41. It will now be assumed that, with the foregoing conditions obtaining, the rotational speed of the support 33 is increased to a value such that F55 increases to a point 33 which is located at the intersection of the line F55 and F51. At this point F55 and F51 are equal and opposed and the arm 43 may be said to be in a state of unstable equilibrium, whereby the application of a minute additional centrifugal force will cause the arm 40 to begin movement away from the stop 41. Such an additional force might be represented as a very slight force upwardly from the point 83 on the line 047, the additional force being so small as to be incapable of illustration in Fig. 6. As aforesaid, the arm 46 begins movement away from the stop 41 thereby decreasing the angles 5 and 0.

As illustrated in Fig. 6, the slope of the line F51 is greater than that of the line F55 so that, although both F55 and F51 decrease as 0 (or It) decreases, F51 decreases at a much higher rate than F55. Consequently, once the arm 40 begins to move toward the stop 46, the force differential moving it toward the stop 46 increases rapidly so that the arm is moved from stop 41 to the stop 43 with a snap action, the maximum value of this force diiferential being attained when the arm engages the stop 46. The maximum value of this force differential is represented by the vertical distance between the points 85 and 8B, the point 85 being at the intersection of the line F55,,,,,, and the line 04a and the point 86 being at the intersection of the lines F51, 64s and F55 In view of the foregoing, it will be apparent that as soon as the centrifugal force F55 increases to a value slightly higher than the spring force F51, the arm 43 moves from the stop 41 to the stop 46 with a snap action because of the fact that the force differential available for moving it toward the stop 45 increases rapidly as it approaches this stop, all of this occurring without any necessity for any increase in the rotational speed of the support 33 above the critical value necessary to initiate movement of the arm. As previously indicated, movement of the arm 40 from the stop 4'! to the stop 43 is communicated to the plunger H to close the switch 56 in the particular construction illustrated.

It will now be assumed that, with the arm 40 in engagement with the stop 43, the rotational speed of the support 33 decreases from the value corresponding to the line F55 As a result, the centrifugal force F55 drops along the vertical line 045. As long as the rotational speed of the support 33 is such that F55 remains at a value higher than that indicated at the point 86, the arm 40 remains in engagement with the stop 46. When the rotational speed drops to a point where F55 is equal to Fss and hence equal to F51, the arm 40 is again in a state of unstable equilibrium, whereby a minute reduction of centrifugal force will cause the arm 43 to begin movement away from the stop 46. Such a force reduction might be represented as a very slight force downwardly from the point 86, the force reduction being so small as to be incapable of illustration in Fig. 6. As aforesaid, the arm 43 begins movement away from the stop 46, thereby increasing the angles and 0. Consequently, since the slope of line F51 is greater than that of F55 the force F51 will increase at a greater rate than F55,,,,,, and the arm 40 will therefore accelerate with a snap action from the stop 46 to the stop 41 with no reduction of rotational speed below the value necessary to initiate movement of the arm. Consequently, the arm 40 moves from stop 46 to the stop 47 with a snap action, the maximum value of the force difierential biasing the arm 40 toward the stop 41 being indicated by the vertical distance between the points 83 and 88 on the line Thus, the arm 40 moves between the stops 46 and 4'! with a snap action in both directions, the arm moving from the stop 41 to the stop 46 with a snap action whenever the rotational speed of the support 33 increases to a critical value corresponding to the line F55,,,,,, and moving from the stop 43 to the stop 41 with a snap action whenever the rotational speed of the support decreases to a critical value corresponding to the line min The foregoing analysis of the operation of the centrifugally-operated snap-action mechanism of the invention has omitted from consideration the effect of the spring force applied to the arm 40 by the spring blade 59 of the switch 56. The variation of the spring force applied to the arm 40 by the spring blade 59 with variations in the angle 6 is graphically illustrated by the dot and dash line 90 in Fig. 6. Since, as previously discussed, a clearance is preferably provided between the arm 40 and the plunger II when the arm is in engagement with the stop 41, the line 90 intersects the horizontal axis of the graph at a point between the vertical lines 046 and 041. The value of the spring force applied to the arm 40 by the spring blade 59 reaches a maximum when the arm 43 is in engagement with the stop 46, i. e., at the point of intersection of the line 90 with the vertical line 045. The sprin forces represented by the line F51 and the line 90 are additive so that the latter has the effect of decreasing the force differential which biases the arm 40 toward the stop 46 and of increasing the rotational speed of the support 33 at which the arm 40 snaps from the stop 45 into engagement with the stop 41. From the foregoing, it is thought that the effects of the spring force applied by the spring blade 59 will be apparent so that any further discussion thereof will be unnecessary.

The foregoing analysis has likewise disregarded the force applied to the arm 40 which is occasioned by bowing thereof as shown in Figs. 1 and '7. As stated hereinbefore, the support 33 may have its surface formed in a manner to eliminate the bowed effect of the arm 40. In such an event the operation of the snap-action mechanism would be substantially as described in the foregoing analysis. If, however, the mechanism is constructed as shown in Figs. 1 and '7, then an additional force due to the bowing of the leaf sprin comprising a portion of the arm 40 will enter into the analysis of the operation of the mechanism. Such additional force is represented in Fig. 6 by the dashed line 99. It is apparent that the value of such a force is additive to the centrifugal forces F55,,,,,,, and F55,,,,,, and is a maximum when the arm 43 engages the stop 41.

In the embodiment of the invention presently under consideration, two adjusting means 91 and 92 are provided for varying the critical speed at which the arm 40 snaps from engagement with the stop 41 into engagement with the stop mum values of both and to vary the critical speed at which the arm snaps from engagement with the stop M into engagement with the stop 46. The adjusting means 92 comprises a plurality of the notches 53 for the springs 51. As will be apparent, shifting the springs 51' from one pair of the notches 53toanother alsova'ries the maximum values of both and 0 to'vary the critical speed at which the arm Mlsnaps from engagement with the stop 4! into engagement with the stop 46.

The embodiment of my invention which is illustrat'ed: in Fig. '7 is substantially identical to that discussed previously and identical reference numerals are employed to designate correspond ing components. fers' from that previously described in' thatthe plunger TI is shown as constantly in engagement with'the arm Ml of the snap-action mechanism and is biased into engagement with the arm it by a compression spring 95which is seated against an extension 96' of the switch blade 59. The spring force applied to'the arm it through the plunger ll by the spring. 95 may bevaried' by'means of a screw 97' against which one end of the spring 95 is seated. The spring force applied to the arm 40 by the spring 95and' the spring force applied thereto by the springs 5i are'additive' and oppose the-centrifugal force applied to the arm upon rotation of the support 33. The effect of the additional spring force provided'by the spring 95' is to change the slope" of' the line F51 discussedpreviously; Also, unless the spring force provided" by the spring95'drops to zero'when the arm 40" engages the 'stop ll, it also has the effect of shifting the line F51 bodily along the horizontal axi's'of the graph of Fig. 6. The operation of the embodiment of Fig. 7 is similar to that described previously and will not be discussed in detail.

The embodiment of Fig. 7 provides a third adjusting means 98 for varying the critical speed at which the arm lfil snaps from engagement with the stop ll into engagement with the stop 46, the adjusting means 98 being the screw 91. As will be apparent, the position of the screw 9'5 may be adjusted to adjust the spring force applied to the arm 46] by the spring 95, thereby varying the aforementioned critical speed. It is also apparent that if the embodiment of Fig. 7 were so constructed that the plunger H did not constantly engage the arm 40, then it would be possible to adjust the switch to change only the lower speed at which the arm 40 moves from the stop 26 to the stop 41, i. e., adjustment of screw 97 would vary the differential between the cut-out and cut-in speeds of the snap-switch mechanism without changing the upper, cut-out speed.

Thus, the present invention provides a'centrifugally-operated mechanism which operates with a snap-action as soon as the rotational speed attains either a maximum or a minimum critical value. I have disclosed my centrifugally-operated snap-action mechanism as used to actuate a switch, but it will be understood that it may be employed to actuate other elements as well. Various other changes, modifications and substitutions may be incorporated in the specific embodiments disclosed without departing from the spirit of the invention.

The embodiment of Fig. 7 dif-' plication to said weight of a centrifugal force;

which biases said arm toward one endof said axis; and a leaf spring in compression connected to said arm' on said opposite side of said axis and pivotally connected" to said support on said one side of said axis for biasing said army toward the opposite end of said axis in opposition to the'acti'on of saidcentrifugal force.

2. In combination: a support having anaxi's of rotation; an arm pivotally connected at one end to said support at one side of: said axis and extending to the opposite side thereof; means including two stops carried by said support" aridr'espectively disposed on opposite sides of said axis of rotation and also on opposite sides of said arm for limiting movement of said ar'm' relative to said" support; spring means connected to said armand said support for applying to said arm a spring force which biases it toward one of said'stops; and adjusting means for shifting thepoint of pivotal connection of said one end" of said arm to'said support.

3; I-n combination": a support having an axis of rotation; anarm pivotally connected at one end to'sa'id support at one side ofslaid axis; said arm'extending totlie'opposit'e side thereof; means including two stops carried by said support and. respectively disposed on opposite sides of said arm-'forlimiting movement of said arm relative to said support; spring means under compression connected'to said arm and said support for applying to' said" arm a spring force which biases it-toward one of saidstops;- and adjusting means for varying the point of connection of said spring means to said support.

4. In a mechanism of the class described: a support having an axis of rotation; an arm pivotally connected at one end to said support, said connection being at one side of said axis and said arm extending to the opposite side thereof; spring means connected to said arm and said support for applying to said arm a spring force which biases it in one direction; and spaced connection points for varying the point of connection of said spring means to said support 5. In mechanism of the class described: a support having an axis of rotation, said support having a plurality of notches spaced longitudinally relative to said axis; an arm pivotally connected at one end to said support and at one side of said axis, said arm extending to the opposite side thereof; stop means for limiting movement in one direction of said arm relative to said support; and spring means connected to said arm and having one end received in one of said notches for applying to said arm a spring force which biases said arm toward said stop means, said one end of the spring means being receivable in the other of said notches for varying the point of connection thereof relative to the support.

6. In mechanism of the class described: a support having an axis of rotation; a resilient arm pivotally connected at one end to said support, said end being at one side of said axis and said arm extending to the opposite side thereof;

means, including two stops, carried by said support and respectively disposed on opposite sides of said arm for limiting movement of said arm relative to said support; and spring means connected to said arm and said support for applying to said arm a spring force which biases said arm against the resilience of said arm toward one of said stops so that said arm is under compression.

7. In mechanism of the class described: a support having an axis of rotation; an arm pivotally connected at one end to said support and free to move relative to said support at its other end, the free end of said arm being at one side of said axis and being adapted to move in one direction under the influence of centrifugal force when the support is rotated; resilient means under compression for biasing said arm in the other direction and putting said arm under longitudinal tension; stop means limiting the movement of the arm in said other direction so that said arm is disposed at an angle of less than 90 relative to said axis when engaging said stop, said resilient means and said arm being arranged so that said arm has a tension center line and said arm being adapted to pass from one side of said line to the other with a snap-action; and stop means limiting the movement of said arm under the influence of centrifugal force, said stop means being located adjacent said center line.

8. In mechanism of the class described: a sup port having an axis of rotation; an arm pivotally connected at one end to said support and free to move relative to said support at its other end, the free end of said arm being at one side or said axis and being adapted to move in one direction under the influence of centrifugal force when the support is rotated; resilient means under compression for biasing said arm in the other direction and putting said arm under longitudinal tension; stop means limiting the movement of the arm in said other direction so that said arm is disposed at an angle of less than relative to said axis when engaging said stop, said resilient means and said arm being arranged so that said arm has a tension center line and said arm being adapted to pass from one side of said line to the other with a snap-action; and stop means limiting the movement of said arm under the influence of centrifugal force short of said center line.

9. In mechanism of the class described for actuation of an electrical switch: a support having an axis of rotation; an arm pivotally connected at one end to said support and free to move relative to said support at its other end, the free end of said arm being at one side of said axis and being adapted to move in one direction under the influence of centrifugal force when the support is rotated; resilient means under compression for biasing said arm in the other direction and putting said arm under longitudinal tension; stop means limiting the movement of the arm to said other direction so that said arm is disposed at an angle of less than 90 relative to said axis when engaging said stop, said resilient means and said arm being arranged so that said arm has a tension center line and said arm being adapted to pass from one side of said line to the other with a snap-action; actuatable means actuated by said arm; and stop means limiting the movement of said arm under the influence of centrifugal force, said stop means being so located adjacent said center line.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,017,571 Lowwenstein Feb. 13, 1912 2,170,748 Eaton Aug. 22, 1939 2,246,724 Eaton June 24, 1941 2,381,931 Shepard et al. Aug. 14, 1945 2,518,478 Kohl Aug. 25, 1950 

